There has been little investigation of speech-like phenomena in the natural vocal communication systems of non-human primates. This research will examine the vocal repertoires of five species of monkeys: Pygmy marmosets, cotton-topped tamarins, talapoin, patas, and stumptail macaques. Seven types of studies will be carried out with each species: (1) A catalogue of the vocal repertoire of each species, (2) analysis of this repertoire to determine whether there are variations in cells (analogous to phonemic variations) that correlate with specific contexts of calling, (3) analysis of repertoires to determine whether consistent individual differences appear in the vocalizations of monkeys, (4) study of the ontogeny of vocal communication in monkeys to determine the developmental natural history of calls, whether adult-like calls appear with the same form and function, whether calls unique to infant animals appear, and whether changes in social development of animals can be correlated with changes in vocal behavior, (5) Playbacks of vocalizations to monkeys to determine whether individual recognition of animals will occur by virtue of vocal cues alone and to determine whether contextually correlated variants in a given call will elicit different responses from recipient animals, (6) development of synthetic representations of natural vocalizations which can be played back to animals with specifiable alterations in acoustic parameters to determine the nature of the perceptual cues important in the reception of a call. We have already shown an analogue to categorical perception in the responses of pygmy marmosets to their vocalizations, (7) development of techniques for recording heart rate which would utilize heart rate deceleration to novel stimuli as a means of measuring a monkey's ability to discriminate between calls using an involuntary response measure. These studies will indicate which primate species show analogues to human speech phenomena and can provide the basis for studies on the physiological basis of speech using non-human subjects.